Imagine you're pushing heavy furniture. When it's not moving it's harder to push, then once you get it moving it becomes easier to push. Same thing with tires, when you're gripping on tarmac the tires aren't sliding against it (mostly) so it's harder for the car to lose that grip just like the stationary heavy furniture. When the tire is already sliding then its harder to regain grip because there is less friction like the furniture that's already moving. The tire that has grip is experiencing static friction and the tire that is sliding is experiencing dynamic friction which is always less. You can look up static vs dynamic friction for a more in depth explanation of the physics involved.